1. Field of the Invention
The present invention relates to an active matrix type display device using a light emitting element in a pixel, a driving method thereof, and an electronic device including this kind of display device.
2. Description of the Related Art
A display device, for example, a liquid crystal display has a large number of liquid crystal pixels arranged in the form of a matrix, and displays an image by controlling the transmission intensity or reflection intensity of incident light in each pixel according to image information to be displayed. This is true for an organic EL display or the like using an organic EL element in a pixel. However, unlike the liquid crystal pixel, the organic EL element is a self-luminous element. The organic EL display has advantages of high image visibility, no need for a backlight, high response speed and the like as compared with the liquid crystal display. In addition, the luminance level (gradation) of each light emitting element can be controlled by the value of a current flowing through the light emitting element. The organic EL display differs greatly from a voltage control type such as the liquid crystal display or the like in that the organic EL display is of a so-called current control type.
As with the liquid crystal display, there are a simple matrix system and an active matrix system as driving systems of the organic EL display. The former system offers a simple structure, but presents, for example, a problem of difficulty in realizing a large and high-definition display. Therefore, the active matrix system is now being actively developed. This system controls a current flowing through a light emitting element within each pixel circuit by an active element (typically a thin-film transistor (TFT)) provided within the pixel circuit. The active matrix system is described in Japanese Patent Laid-Open No. 2003-255856, Japanese Patent Laid-Open No. 2003-271095, Japanese Patent Laid-Open No. 2004-133240, Japanese Patent Laid-Open No. 2004-029791, Japanese Patent Laid-Open No. 2004-093682 and Japanese Patent Laid-Open No. 2006-215213.